DESCRIPTION (Scanned from the applicant's description): Increasing numbers of infants are enjoying the benefits of breast feeding for longer and longer periods. Prolonged breast feeding is relatively uncharted territory from a nutritional point of view. Iron nutrition is one area where there has been concern. Iron stores present at birth provide all the iron the normal infant needs for growth during the first 5-6 months of life. But after iron stores are exhausted the infant depends on a dietary source of iron. Breast milk alone provides only a fraction of the iron the infant needs for growth. Complementary foods vary widely in content of available iron, and it appears unlikely that infants always receive the necessary amounts of iron. The presumption that prolonged breast feeding engenders a risk of iron deficiency was born out by a pilot study. After 6 months of age several infants became iron deficient and some even became anemic due to iron deficiency. Provision of medicinal iron from 1 to 5 1/2 months of age did not improve iron status. Other studies in our unit have shown that infants re-excrete into the stool appreciable amounts of absorbed iron. This proposal builds on these earlier studies. In Specific Aim 1 we propose to generate a broad picture of the iron nutritional status of breast-fed infants (specifically, infants who are breast-fed for prolonged periods) and of the complementary foods they are fed and the amount of iron they derive thereof. Infants will be studied longitudinally from 1 to 24 months of age. From a public health point of view there is an urgent need for this information because it will delineate the magnitude and the nature of the problem. Equally urgent is the need to find ways of preventing iron deficiency. The objective of Specific Aim 2 is to explore the efficacy of two different regimens of iron supplementation. One is the provision of medicinal iron (iron drops), the other is the feeding of one jar per day of an iron-fortified cereal-fruit combination, both from 4 to 9 months of age. We expect these regimens to be effective and the beneficial effects to persist beyond the supplementation period. Specific Aim 3 is concerned with the mechanisms that allow most breast-fed infants to remain in good iron status despite the low iron content of breast milk. We also hope to solve the puzzle why iron supplementation was ineffective in the young infants in our pilot study. We will use two stable (non-radioactive) isotopes of iron to determine absorption and excretion of iron by breast-fed infants both at 4 and 9 months of age and with and without iron supplementation. We expect to find that infants re-excrete iron into the feces when their iron stores are full, but retain most of the absorbed iron when iron stores are low.